1. Not bothering to apply because you're sure you won't get the job. Sure, if it's a wild reach, put your time into other opportunities. But if you can make a reasonable case for yourself, then you shouldn't write off an opening just because you assume that others will be better qualified than you. For some jobs, hiring managers may be willing to take a risk on a less-experienced candidate who brings other strengths. You'll never find out if you don't try.

2. Obsessing over your resume and cover letter, to the point that you miss application deadlines or don't apply at all. It doesn't matter how perfect your cover letter is if no one ever sees it. If you tend to agonize and put off applying while you work to get things "perfect," set yourself a time limit: No more than 30 minutes spent per cover letter, and once you start writing one, you must send it that same day.

3. Not bothering with a cover letter at all. If you're applying for jobs without sending in a cover letter, you're missing out on one of the most effective ways to grab an employer's attention. A cover letter gives you a chance to make a compelling case for yourself as a candidate, totally aside from what's on your resume. Some job seekers convince themselves that because some hiring managers don't read cover letters, none of them do—which is far from true. At a time when most job seekers are wondering how they can stand out in a crowded field, a great cover letter is one of the best ways to strengthen your chances of getting noticed.

4. Being shy about telling people that you're looking for a job.If you're hesitating to let your network, family, and friends know that you're looking for work, hesitate no longer. There's no shame in being on the job market; it's very common, and most people are glad to help if they can. So let people know that you're looking! You never know who in your network might know of an opening for which you'd be perfect.

5. Getting defensive about a job that didn't work out. If you're asked about a job from whichyou were fired, you don't need to give an exhaustive account of what happened. Most interviewers are only looking for a few sentences and won't expect a detailed account. Be brief and to the point, upbeat, and don't sound defensive or angry.

6. Being bitter and letting it show. It's easy to start feeling pessimistic if you put a lot of time into applying for jobs and it hasn't paid off with an offer. But if you're bitter, it'll almost certainly show when you talk to employers, and that will kill your candidacy faster than a spotty resume or bad interview answer ever could.

7. Not showing your enthusiasm for the job. Sometimes I interview a candidate and end up unsure if she's even particularly interested in the job. If you're excited about the job, say so! Hiring managers are human—we like it when we feel a real interest from you.

8. Being too quick to assume that you're out of the running, so not following up. After a job interview, do you obsess over all the little mistakes you think you made, and beat yourself up for not giving different answers? Some people take this to such an extreme that they decide they obviously failed the interview, and so they don't bother to do any follow-up. Obsess if you must, but don't let it deter you from following up after the interview to reiterate your interest. Your self-assessment may not line up with theirs.